ARM: dts: rockchip: readd missing mmc0 pinctrl settings

During the restructuring of the Rockchip Cortex-A9 dtsi files it seems
like the pinctrl settings vanished at some point from the mmc0 support.

This of course renders them unusable, so readd the necessary pinctrl
properties.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>